Dental amalgams are produced by intimately combining mercury with dental amalgam alloys, such as an alloy containing about 55-75% by weight silver, 20-40% tin, 0-10% copper and 0-2% zinc. Upon reaction with mercury using known dental clinical techniques, a plastic mass is produced which quickly sets into a hard rigid body. While the mass is plastic, it may be packed into a surgically prepared tooth and carved or otherwise worked into a desired conformation, thereby restoring the anatomy and function of the tooth.
Heretofore such alloys consisted of powder in the form of irregularly-shaped microgranules, flakes or filings or powder in the form of spheroidal particles. The trend toward use of spheroidal powder was generated by the dentists' desire to reduce packing pressure or condensation and to minimize the amount of mercury required in the amalgamation of the powder. Amalgams made from spheroidal particles also have the desirable attribute of a higher diametral tensile strength than amalgams made from microgranules, flakes or filings and also generate less expressed mercury prior to placement in tooth cavities.
Amalgams made from spheroidal powder, however, exhibit an undesirable feature. When the dentist attempts to pack them within a cavity there is a tendency for the amalgam to ride up along walls of cavity and not pack as firmly as amalgams made from filings or microgranules.